def prost(x):
    for i in range(2,x):
        if x % i == 0:
            return 0
        return 1
print('Введите четырехзначное натуральное число')
s = int(input())
kol_pr = 0
max_pr = 0
if s >= 1000 and s < 10000:
      s=str(s)
      x=s[0]
      if prost(int(x)) == 1:
          kol_pr+=1
          max_pr = max(max_pr,int(x))
      x=s[1]
      if prost(int(x)):
          kol_pr+=1
          max_pr = max(max_pr,int(x))
      x=s[2]
      if prost(int(x)) == 1:
          kol_pr+=1
          max_pr = max(max_pr,int(x))
      x=s[3]
      if prost(int(x)) == 1:
          kol_pr+=1
          max_pr = max(max_pr,int(x))
      x=s[0]+s[1]
      if prost(int(x)) == 1:
          kol_pr+=1
          max_pr = max(max_pr,int(x))
      x=s[1]+s[2]
      if prost(int(x)) == 1:
          kol_pr+=1
          max_pr = max(max_pr,int(x))   
      x=s[2]+s[3]
      if prost(int(x)) == 1:
          kol_pr+=1
          max_pr = max(max_pr,int(x))   
      x=s[0]+s[1]+s[2] 
      if prost(int(x)) == 1:
          kol_pr+=1
          max_pr = max(max_pr,int(x))   
      x=s[0]+s[1]+s[2]+s[3]
      if prost(int(x)) == 1:
          kol_pr+=1
          max_pr = max(max_pr,int(x))
      if kol_pr > 0:
           print(max_pr)
      else:
           print(0)
else:
    print(0)







































